Driving connection control system

ABSTRACT

An automatic transmission comprises a hydraulic torque converter, a clutch unit and a planetary gear unit. The clutch unit is provided with a braking unit. Hydraulic pressure corresponding to the reaction torque of the braking unit is produced and used for engaging the braking unit.

United States Patent Higuchi et al. 1451 Mar. 21, 1972 [5 DRIVINGCONNECTION CONTROL 1 References Cited SYSTEM UNITED STATES PATENTS [72]Inventors: Toshio Higuchi, Suita-shi; Hldeyuki 2 946 24 17/1960 S d yner "74/751 X '3 :f 3,230,792 1/1966 Kelley et a1. ...74/75] x s a3,251,245 5/1966 Forster ..74/751 [73] Assignee: Mitsubishi JldoshaKogyo Kabushlkl 3,251,246 5/1966 Forster et a1 ..74/751 Kaishn,Minato-ku, Tokyo, Japan 3,381,547 5/1968 Forster et al.. ..74/751 X2,896,478 7/1959 Winchell 74/868 X [22] 1969 3,053,107 9/1962 Winchell..74/868 1211 Appl. No.: 860,864

Primary Examiner-Arthur T. McKeon Foreign Application Priority DataA'mmey McG]ew and Tums Sept. 28, 1968 Japan ..43/6997l [57] ABSTRACT[52] U S CL "74/752 74/751 74/868 An automatic transmission comprises ahydraulic torque con- /42 F161] 7 6 2 1/10 verter, a clutch unit and aplanetary gear unit. The clutch unit Field of Search ..74/8 68, 752, 751is Provided with braking "Ydraulic Pressum GOVERNOR VALVE responding tothe reaction torque of the braking unit is produced and used forengaging the braking unit.

7 Claims, 5 Drawing Figures SECONDARY PR. VALVE 22 p 22' 11s s 111 2a,48 151 SPEED I26 119 120 113 DISCRIMINATOR' a?" 6 101 a 185 157' (179T'QUARJE 191" 0 220 lzlgo @196 95 10410? T 1 09 I66 11a 39 L 34/ 1 103|8l '84 I83 T ENGINE I54 I57 BRAKING 160 '59 DISCRIMINATOR r SHIFT I50 J9 6| VALVE 5 2 I '36 15 I62 I64 THROTTLE 131 132 146 153 141 I63 I! I56'48 w 16! 33 63 E P56 145 r 79 e2 e1 I43 1:59 84 7 87 5 T 2 a3 68 77 4s73 74 15 7e 9i 85 9 81 ,r 66 86 94 82 i H R 1 i 1 SZRIMARY 45 76 7O LDN57 FPRVALVE VALVE PATENTEDMARZI I972 3,650,160

sum 1 0F 3 INVENTORS TOSHIO H/G-ucm Hnbeyum HNFIBE 114x50 HIRHMFIT'sU BYWW dow 737w ATTORNEYS PATENTEDMAR21 I972 3,650,160

SHEET 3 OF 3 FIG. 3

SEC REGULATING PRESS. kg/m -2 o 2 4 e B IO DRUM venous kq-m FIG. 4

(AT ENG-BRAKING FIRST SP) kq TER REGULATING PRESS.

ON-bmco'GE-EE SP 0F OUTPUT SHAFT rpm INVENTORS FPS/410 H 16 u c H/ H/D6) Wu M/VHBE THAED MR3 HF! T5 U BYVMWMTZZ ATTORNEYS DRIVING CONNECTIONCONTROL SYSTEM BACKGROUND OF THE INVENTION This invention relates to asystem for controlling a driving connection between a driving shaft anda driven shaft, and more particularly to a hydraulic control systemadapted for use with automatic transmissions for vehicles.

One conventional automatic transmission for vehicles has been soconstructed that a hydraulic pressure (line pressure) supplied to thefriction mechanism of the transmission is regulated in dependence uponthe vehicle speed and the throttle opening. In another transmission, thehydraulic pressure is regulated in dependence upon the reaction torqueof the stator of a torque converter. Accordingly, at a low vehicle speedand a large throttle opening, the line pressure applied to the frictionmechanism, owing to a large torque to be transmitted, is in generalselected higher, while either at a high vehicle speed or at a smallthrottle opening the line pressure is selected lower. This is due to thefact that, when the hydraulic pressure for gear change is higher thanrequired, a large shock at gear change appears and the power loss in theoil pump become disadvantageously large.

In a conventional control system, the line pressure is kept nearlyconstant for a short period at gear change, and it is very difficult totime ideally the relief of hydraulic pressure from one frictionmechanism and the supply of hydraulic pressure to the other frictionmechanism. Therefore, a one way clutch is generally used in the firstspeed section of a forward three speed type transmission, so that at thegear change from the first speed to the second speed it is not necessaryto relieve the hydraulic pressure from the friction mechanism and it isonly necessary to control the building-up speed of hydraulic pressurefor the friction mechanism corresponding to the second speed, thusmaking the control easy. On the contrary, the gear change from thesecond speed to the third speed and that from the third speed to thesecond speed, which are both carried out by means of the frictionmechanism, are controlled with difficulty.

Particularly in a forward two speed type transmission, the provision ofa one way clutch is disadvantageous because it increases the costthereof almost to that of a three speed transmission. Accordingly boththe first speed and the second speed must be established by the use offrictional mechanisms. Thus the timing for supplying the hydraulicpressure becomes difficult.

In a transmission having a torque converter and regulated in dependenceupon the vehicle speed and the throttle opening, the line pressure mustbe raised up twice as high as the pres sure in a usual high speedoperation, because the increase in torque at a low vehicle speed is ofconsiderable magnitude. For this purpose, a special consideration forthe line pressure at a low speed is often given. For example, in orderto increase the line pressure at a low speed the throttle pressuredepending upon the throttle opening is applied to a pressure regulatorvalve and at the same time the re-regulated throttle pressure is appliedagain to the pressure regulator valve to raise the pressure while theaction of this re-regulated pressure is interrupted at a high speed. Thepressure may be raised by exerting the reaction torque of the stator ofa torque converter upon the pressure regulator valve.

As described above, while the line pressure must be delicately changedin dependence upon the vehicle speed and the throttle opening,nevertheless its control in the conventional systems is not easy andrequires additional valves.

SUMMARY OF THE INVENTION The principal object of this invention is tosolve the aforesaid problems of control of power transmission.

In accordance with the invention, a fixing friction mechanism isprovided on an intermediate rotary member, in a transmission mechanismbetween a driving shaft and a driven shaft, in order to control adriving connection between both shafts. A hydraulic pressurecorresponding to the reaction torque due to a fixing friction is usedfor engaging the friction mechanism in such a manner that it is raisedwith an increase of the torque in one direction of rotation to completethe engaging of the friction mechanism while it is held so low in theother direction of rotation as not to establish the engaging of thefriction mechanism so that the engaging of the fixing friction mechanismis established only in a predetermined direction like in a one wayclutch. Thus the shock at the time of gear change may be mitigated. Byadoption of the mechanism according to the invention it may beimpossible that a torque is transmitted from the driven shaft to thedriving shaft at the time of engine braking. By provision of a drivediscriminating device such as an engine braking discriminator valvewhich discriminates a driving relation between the driving shaft and thedriven shaft, a hydraulic pressure which rises with increase of thevehicle speed independently of the torque transmitted may be produced bymeans of another pressure regulator valve at the time of engine brakingand then supplied to the fixing friction mechanism for the engagingthereof. Thus the fixing friction mechanism operates as a one way clutchonly during gear change.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 shows in schematic form an automatic transmission embodying thepresent invention;

FIG. 2 is a schematic view of a hydraulic control circuit capable ofbeing used with the transmission of FIG. 1;

FIG. 3 is a graph showing the relation between the regulating pressureand the torque of the transmission;

FIG. 4 is a graph showing the relation between the regulating pressureand the speed of the output shaft; and

FIG. 5 is a cross-sectional view of the gear unit taken along line V-VofFlG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1, 2 and5 a transmission has a driving shaft (input shaft) 10, a driven shaft(output shaft) 11 and an intermediate shaft 12 arranged in alignmentwith one another. The transmission is composed of a hydraulic torqueconverter 13, a planetary gear unit (Ravigneaux-type) 14, a

brake 15 for the first speed, a clutch 16 for the second speed, and abrake 17 for the backward speed. The torque converter 13 consists of animpeller with blades (pump) 18, a driven runner with blades (turbine)19, and a reaction member with blades (stator) 20.

The pump 18 is connected to the driving shaft 10 by means of a convertercasing 21, while the turbine 19 is connected to the intermediate shaft12. The stator 20 is connected to a sleeve shaft 23 through a one wayclutch 22, the sleeve shaft 23 being secured to the main body of thetransmission as shown. The torque converter is of a conventionalconstruction.

The planetary gear unit 14 is composed of a front sun gear 24, a rearsun gear 25, long pinions 26, short pinions 27, a ring gear 28, andplanetary carriers 29. The from sun gear 24 is formed integral with asleeve shaft 30 and meshes with short pinions 27, which in turn meshwith the long pinions 26 and the ring gear 28. The long pinions 26 meshwith the short pinions 27 and the rear sun gear 25. The rear sun gear25, which is driven by the intermediate shaft 12, meshes with the longpinions 26.

The second speed clutch 16 arranged within a drum 36 consists of clutchplates 31, 32, a pressure plate 33, a piston 34, and a return spring 35.The clutch plates 31 are carried on the internally splined drum 36 whilethe clutch plates 32 are carried on a splined clutch hub 37.Accordingly, the turbine 19, the intermediate shaft 12, the clutch hub37, the clutch plates 32 and the rear sun gear 25 rotate as one body,while the drum 36, the piston 34, the return spring 35, the clutchplates 31, the pressure plate 33, the sleeve shaft 30 and the front sungear 24 also rotate as one body.

The piston 34, when a hydraulic pressure is applied to the cavity 38 ofthe drum 36 from a pressure line 39, engages, against the return spring35, the clutch plates 31 with the clutch plates 32. When the hydraulicpressure is relieved from the cavity 38, the piston 34 is returned bythe return spring 35 to disengage the clutch plates 31 from 32 from oneanother. When the clutch plates 31 frictionally engages the clutchplates 32, a direct driving connection is established between theintermediate shaft 12 and the sleeve shaft 30 so that the front sun gear24, the rear sun gear 25, and thus the output shaft 11 rotate at thesame speed. In this case the reduction ratio of the intermediate shaft12 to the output shaft 11 is equal to l.

The reverse brake 17, when applied with a hydraulic pressure from apressure line 40, holds the ring gear 28 with the aid of a servo piston(not shown). In this instance, since the other brake and the clutch arereleased, the intermediate shaft 12 rotates in a direction opposite tothe output shaft 11 so that the reduction ratio will be equal to l .82.

The drum 36 and the first speed brake 15, as illustrated in FIG. 2, areviewed from the front side of the automatic transmission or from thetorque converter side.

The first speed brake 15 brakes the drum 36, when a hydraulic pressureis applied to a cavity 206 of a servo unit 110 from a pressure line 199to urge a piston 202 against the force of a return spring 204. The frontsun gear 24 is then held stationary so that the reduction ratio of theintermediate shaft 12 to the output shaft becomes equal to 1.82.

The output shaft 1 1 may be connected to the driving wheels of a motorvehicle by a suitable means (not shown).

A governor 44 is secured to the output shaft 11 to rotate therewith, andis capable of producing a hydraulic pressure in accordance with therotating speed thereof.

FIG. 2 illustrates a hydraulic control system for the automatictransmission shown in FIG. 1. This control system comprises thefollowing valves:

Manual valve 45 Primary pressure regulator valve 46 Secondary pressureregulator valve 47 Tertiary pressure regulator valve 48 Throttle valve49 Shift valve 50 Governor valve 51 First speed discriminator valve 52Engine braking discriminator valve 53 Besides the above valves, thecontrol system includes an oil pump 54 driven by the engine.

Oil from an oil sump (not shown), after being cleared of dust particlesby means of an oil strainer 55, flows into the oil pump 54 through aline 56 and is then fed through a line 57 to the primary pressureregulator valve 46, the manual valve 45 and the throttle valve 49.

The primary pressure regulator valve 46 is connected through a line 58to the secondary pressure regulator valve 47, which in turn is connectedto the tertiary pressure regulator valve 48 through a line 59. Thetertiary pressure regulator valve 48 is connected to parts to belubricated, through a line 60, and to the torque converter 13.

The throttle valve 49 is connected to the engine braking discriminatorvalve 53 by a line 61 and also connected to the shift valve 50 through acheck ball 62 and a line 63.

The shift valve 50 is connected to the cavity 38 of the second speedclutch 16 through a line 39 and also connected to the first speeddiscriminator valve 52.

The manual valve 45, which is used for selecting various drivingconditions, consists of a cylindrical bore 64 in a casing 65 with avalve piston 66 movable in the cylindrical bore 64. The casing 65 isprovided with ports 67, 68, 69, 70, 71 and 72, all of them opening tothe bore 64. The valve piston 66 is formed with lands 73, 74 and 75,with has annular grooves 76,

77 and 78 therebetween. The ports 69 and 70 are connected The valvepiston 66 is capable of selectively taking any of five positions uponits axial movement to communicate the desired ports with each other inaccordance with the selected position. The five positions are theposition P, for parking and engine-starting, the position R, for reverseoperation, the neutral position N, the automatic gear change position Dbetween the first speed and the second speed, and the position L for thefixed first speed. The valve piston 66 as shown is in the neutralposition N.

The primary pressure regulator valve 46 has the function of regulatingthe hydraulic pressure developed by the pump 54, and includes a casing82 having a stepped cylindrical bore 81 formed therein, a valve piston83, a valve plug 84 and a valve spring 85. The casing 82 is providedwith ports 86, 87, 88, 89, and 91, all of them opening to the bore 81.The valve piston 83 is formed with lands 92, 93, 94 and 95, and hasannular grooves 96 and 97 between the last three lands. The ports 86, 91are exhaust ports for the oil sump. The port 87 is connected to the line40, the port 88 to the line 58, the port 89 to the line 57, and the port90 to the line 57 through an orifice 98, respectively. The primarypressure regulator valve 46 acts only when the hydraulic pressure in theline 58 is lower than the regulated pressure regulated by this valve,and loses its function when the hydraulic pressure in the line 58 ishigher than the regulated pressure. In the latter case, the hydraulicpressure in the line 57 or 58 will be regulated by the secondarypressure regulator valve 47 or the tertiary pressure regulator valve 48.

The pressure regulated by the primary pressure regulator valve 46 is setto, for instance, 5 kg./cm."' in forward operation and l2 kg./cm. inreverse operation.

The secondary pressure regulator valve 47, which has the function ofdeveloping a hydraulic pressure corresponding to the torque generated inthe drum 36 in a direction designated with an arrow, is composed of acasing with a cylindrical bore 99 formed therein, a valve piston 101, avalve plug 220, a valve spring 221, a resiliently biased abutment member224 and a lever 222 for transmitting the torque produced by the drum 36and an adjusting screw 223. The casing 100 is provided with ports 102,103 and 104, all of them opening to the bore 99. The valve piston 101 isformed with lands and 106, and has an annular groove 107 therebetween.The port 102 is connected to a line 108, the port 103 to the line 58,and the port 104 to the line 59. The line 108 is connected to the line58 through an orifice 109. The pressure regulated by the valve 47amounts to a value corresponding to the torque produced by the drum 36only when the regulated pressure is higher than the pressure of the line59 regulated by the tertiary pressure regulator valve 48, while thepressure in the lines 58 or 108 will be equal to the pressure regulatedby the tertiary pressure regulator valve 48 when the regulated pressureof the valve 47 is lower than the pressure regulated by the tertiarypressure regulator valve 48.

The tertiary pressure regulator valve 48 is provided for the purpose ofmaintaining the hydraulic pressure applied to the servo unit 110 higherthan the regulated pressure of the secondary pressure regulator valve 47to establish the frictional engagement of the first speed brake 15 atengine braking and for feeding the oil to the torque converter 13 aswell as to the parts to be lubricated. The valve 48 is composed of acasing 112 with a stepped cylindrical bore 111 formed therein, a valvepiston 113 and a valve spring 114. The casing 1 12 is provided withports 115, 116, 117, 118, 119, 120, and 121, all of them opening to thebore 111. The piston 113 is formed with lands 122, 123, 124 and 125, andhas annular grooves 126, 127 and 128 therebetween. The ports 116 and 121are exhaust ports for the oil sump. The port is connected to a line 129,the ports 117 and 119 to the line 59, the port 118 to the line 60, andthe port 120 to the line 59 through an orifice 130, respectively. Theline 60 is an oil feeding pipe to the torque converter 13 and the partsto be lubricated.

The throttle valve 49, which has the function of producing a hydraulicpressure corresponding to the throttle opening of the engine, is usedfor determination of the gear change pattern between the first speed andthe second speed and for discrimination of engine braking. This valve 49is composed of a casing 132 with a stepped cylindrical bore 131 formedtherein, valve pistons 133, 134, valve springs 135, 136 and a lever 137.The casing 132 is provided with ports 138, 139, 140, 141, 142 and 143,all ofwhich open to the bore 131.

The piston 133 makes a displacement in dependance upon the throttleopening through the lever 137. The valve piston 134 is formed with lands144 and 145, and has an annular groove 146 therebetween. The valvespring 135 is disposed between the piston 133 and the valve piston 134.The ports 138, 139 and 143 are oil discharge ports. The port 140 isconnected to the line 57, the port 141 to the line 61, and the port 142to the line 61 through an orifice 146. The higher of the pressures inthe line 61, and in the line 79 while urging away the check ball 62,communicates with the line 63.

The shift valve 50 has the function of performing gear change betweenthe first speed and the second speed in dependence upon the vehiclespeed and the throttle opening, but in the low range L the gear is fixedat the first speed. This valve is composed of a casing 148 with astepped cylindrical bore 147 formed therein, a valve piston 149 and avalve spring 150. The casing 148 is provided with ports 151, 152, 153,154, 155, 156, 157, 158 and 159, all of which open to the bore 147. Thepiston 149 is formed with lands 160, 161, 162, 163 and 164, and hasannular grooves between the respective lands as shown. The ports 151 and152 are connected to the line 63, the port 153 to the line 79, the port154 to the line 80 through an orifice 165, the port 155 to the line 39,the port 157 to the line 129, the port 158 to the line 167, and the port159 to the line 166. The port 156 is an oil discharge port for the oilsump. The shift valve 50 shown is in a position for the first speed, andit, when moved leftwards, takes a position for the second speed.

The governor valve 51, which rotates together with the output shaft 11,has the function of producing a hydraulic pressure corresponding to theangular velocity of output shaft 11, or the vehicle speed, due to acentrifugal force. This valve is composed of a casing 169 with a steppedcylindrical bore 168 formed therein, a valve piston 170, a weight 171and a valve spring 172. The casing is provided with ports 173, 174 and175, all of which open to the bore 168. The piston 170 is formed withlands 176 and 177, and has an annular groove therebetween. The port 173is connected to the line 80 and the port 174 to the line 166. The port175 is an oil discharge port for the oil sump. A governor pressureproduced by the governor valve 51 is applied to the shift valve 50 andthe engine braking discriminator valve 53. At engine braking, the line166 is connected to the line 167, and, in case of the first speed, theline 167 is connected to the line 129, whereby the regulated pressure inthe tertiary pressure regulator valve 48 increases with increase of thevehicle speed.

The engine braking discriminator valve 53 has the function of decidingwhether the engine braking is being applied or not by opposing thethrottle pressure to the governor pressure. This valve is composed of acasing 179 with a stepped cylindrical bore 178 formed therein and avalve piston 180. The casing 179 is provided with ports 181, 182, 183and 184, all of which open to the bore 178. The piston 180 is formedwith lands 185 and 186, and has an annular groove 187 therebetween. Theport 182 is connected to line 167, the port 181 to the line 166, and theport 184 to the line 61. The port 183 is an exhaust port for the oilsump. in the state shown the engine is running, and, if the piston 180is moved rightwards, the valve comes into the engine braking range.

A first speed discriminator valve 52 has the function of completelyreleasing the first speed brake in N, R and P ranges, of establishing ahydraulic connection to the servo 1 10 so that the pressure regulated bythe secondary pressure regulator valve 47 may be applied to the servo110 at the first speed in D and L ranges and of relieving the pressureof the servo 110 to prevent the dragging of the first speed brake whenthe shift valve 50 is in the position corresponding to the second speedso that the hydraulic pressure for the second speed clutch increases toa certain extent. The first speed discriminator valve 52 is composed ofa casing 188 with a cylindrical bore 187 formed therein, a valve piston189 and a valve spring 190. The casing is provided with ports 191, 192,193, 194 and 195, all of which open to the bore 187. The piston isformed with lands 196, 197 and 198, and has annular grooves between thelands. The port 191 is connected to the line 39, the port 193 to theline 199, the port 194 to the line 108, and the port 195 to the line 80.The port 192 is an exhaust port for the oil sump.

The servo 110, which has the function of engaging and releasing thefirst speed brake 15, is composed of a casing 201 with a cylindricalbore 200 formed therein, a piston 202, a push rod 203, a return spring204 and a cover 205. The cavity 206 is applied with a hydraulic pressurefrom the line 199.

The device constructed above operates as follows:

The engine is started in the state that the manual valve 45 ispositioned in P position or N position as shown in the drawing. The oilpump 54 is driven with engine running, and oil, after being cleared ofdust by the oil strainer 55, is supplied to the oil pump 54 through theline 56. The oil from the pump is supplied to the ports 89 and of theprimary pressure regulator valve 46, the port 140 of the throttle valve49, and the ports 69 and 70 of the manual valve 45 through the line 57.The piston 83 is moved leftwards by a force produced by the differencebetween the pressures acting on the lands 94 and of piston 83 of theprimary pressure regulator valve 46 against the force of the spring 85.With the leftward movement of the piston 83, the port 88 opens to theline 58 so that the oil flows into the port 103 of the secondarypressure regulator valve 47. When the land 93 to the line 58 is opened,the hydraulic pressure of the line 57 decreases, and is regulated untilthe force of the spring 85 is balanced with the pressure due to thedifferential area between the lands 94 and 95.

Similarly, pressure regulation is carried out in the secondary pressureregulator valve 47, and the pressure oil thus regulated is supplied tothe ports 117, 1 19, and of the tertiary pressure regulator valve 48.Here, the pressure also is regulated until the hydraulic pressure actingon the differential area between the lands 124 and is balanced with theforce of the spring 1 14.

The pressure regulated in the primary pressure regulator valve 46 iskept at 5 kg./cm. in the ranges other than the reverse R range in whichit has a value of 12 kgJcm In the secondary pressure regulator valve 47there appears a hydraulic pressure due to the torque of drum 36 at thefirst speed, but the pressure is kept at a constant valve of 2 kg./cm.in other conditions. FIG. 3 shows the variation of regulator pressure inthe secondary pressure regulator valve 47. When engine brakingdiscriminator valve 53 is moved to the right by the increase of governorpressure, and the apparatus determines that the vehicle speed is withinthe limits of engine braking, and also when the total of the forces ofvalve spring and the fluid pressure acting to the right is larger thanthe force acting to the left, due to governor pressure, and the shiftvalve 50 is maintained in the right-hand position, in the state of thefirst speed, governor pressure from port 174 is applied to port 115 oftertiary pressure regulator valve 48 through lines 166, 167 and 129.Thus, the tertiary regulator pressure is increased with an increase inthe vehicle speed. FIG. 4 shows the variation of regulated pressure inthe tertiary pressure regulator valve 48.

When the manual valve 45 is set for D position, the oil pressureregulated by the primary pressure regulator valve 46 enters into theport 69 and is supplied from the port 68 to the governor valve 51, theshift valve 50 and the first speed discriminator valve 52 through theline 80. As the governor pressure rises with increase of the vehiclespeed, the shift valve piston 149 moves leftwards thus to establish thesecond speed condition. Then, the hydraulic pressure regulated by theprimary pressure regulator valve is fed to the line 39. When thepressure in the line 39 sufficiently rises, the first discriminatorvalve 52 moves rightwards thereby to entirely relieve the hydraulicpressure of the servo 110.

Since the response of a hydraulic pressure at the time of gear change issufficiently quick with respect to the torque variation of the drum 36,there occurs only a small resistance when the drum 36 begins to rotateclockwise in the drawing after the clutch 16 has been applied.Accordingly, the device performs the function of a one way clutch. Atthe kick down at which the accelerator pedal is depressed deeply in thesecond speed condition so that the throttle pressure is greatlyincreased, the line 61 receives a pressure equal to the primaryregulator pressure, whereby the down shift from the second speed to thefirst speed may be carried out below a certain vehicle speed. Since theport 155 of the shift valve 50 communicates with the port 156, theclutch pressure of the line 39 then suddenly decreases so that the firstspeed discriminator valve 52 moves leftwards to connect the port 194with port 193 thereby supplying a hydraulic pressure to the cavity 206of the servo 110 through the line 199. On the other hand, since the drum36 is rotating clockwise, the torque becomes negative, and, as is clearfrom FIG. 3, the secondary regulator pressure rises only up to 2 kg./cmTherefore, dragging due to the brake 15 may be minimized to zero. Whenthe engine speed increases to raise the angular velocity of theintermediate shaft 12 so that the driving relation between respectivegears in the planetary gear unit 14 establishes the first speedcondition and the drum 36 begins to rotate in the direction denoted witharrow, the secondary regulator pressure suddenly increases to hold thedrum 36 stationary. As the servo 110 is so designed that the force ofreturn spring 204 may be balanced with the that of the piston 202 at asecondary regulator pressure of 2 kg./cm. no dragging torque appears solong as the drum 36 is rotating.

When the manual valve 45 is set for L position, the ports 67,

68 and 69 are communicated with one another so that the primaryregulator pressure is applied to the line 79 in addition to the case ofD position. Then, the piston 149 of the shift valve 50 occupies therightmost position to maintain the first speed condition. Further, whenthe manual valve 45 is set for L position during high speed running asfar as it is in the range of engine braking, the tertiary pressure risesso high, as shown in FIG. 4, by the action of the engine brakingdiscriminator valve 53, that the secondary pressure and primary pressurebecome equal to the tertiary pressure and also the hydraulic pressure inthe cavity 206 of the servo 1 also increases. Consequently gear changemay be quickly performed. In the range other than the engine brakingrange, the same condition as kickdown in D position is obtained.

When the manual valve 45 is set in R position, the port 70 iscommunicated with the port 71 to feed a hydraulic pressure to the port87 of the primary pressure regulator valve 46 through the line 40. Theprimary regulator pressure rises higher due to the differential areabetween the lands 92 and 93, and remains at a value of about 12 kg./cm.This primary regulator pressure is supplied to the servo (not shown) ofthe reverse brake 17 (FIG. 1) to hold the brake 17 stationary.

As has been explained, according to the present invention, in thetransmission between the driving shaft and the driven shaft an optimumand accurate control can be performed, and the shock at the time of gearchange is largely mitigated so that a comfortable feeling of gear changemay be obtained. Moreover, owing to provision of a drive discriminatingdevice in connection with transmission control, a very quick responsefor the gear change to the low speed at engine braking is obtainedwhereby defects in engine braking which have so far been considered asone of serious problems in conventional transmissions can be eliminated.

While the form of the control system herein described constitutes apreferred embodiment of the invention, it is to be understood that theinvention is not limited to this embodiment, and that changes may bemade without departing from the scope of the invention which is definedin the appended claims. For instance, instead of the brake band as afixing friction mechanism a clutch may be employed. The presentinvention may be applied not only to automatic transmissions of vehiclesbut also to hydraulic equipment provided with a hydraulic one way clutchmechanism.

What is claimed is:

1. In a transmission mechanism including a driving shaft, a drivenshaft, and change speed gearing interconnecting the shafts, theimprovement comprising, in combination, said gearing including rotatablemembers controlling the speed ratios between said driving and drivenshafts; respective friction means selectively engageable with saidmembers to arrest rotation thereof to select said speed ratios; a sourceof hydraulic fluid under pressure; respective hydraulic actuatorsconnected to said source to control engagement of the associatedfriction means with the respective rotatable members to effect gearchanges; at least a first member of said rotatable members exerting areaction torque on its associated first friction means only whenrotating in a first direction, and exerting substantially no reactiontorque on said first friction means when rotating in the oppositedirection; a control valve regulating the pressure supplied from saidsource to the hydraulic actuator of said first friction means, andnormally maintaining such regulated pressure at a relatively lowpreliminary value; and means operatively connecting said first frictionmeans to said control valve and operable, responsive to exertion of areaction torque on said first friction means, to adjust said controlvalve in correspondence with the magnitude of such reaction torque tosupply, to the hydraulic actuator of said first friction means, aregulated pressure adjusted in direct proportion to the magnitude ofsuch reaction torque to obtain full frictional engagement of said firstfriction means with said first rotatable member to arrest rotation ofthe latter; said first rotatable member having a free-wheeling operationwhen rotating in such opposite direction.

2. In a transmission mechanism, the improvement claimed in claim 1, inwhich said first rotatable member is a drum and said first frictionmeans is a brake band engageable with said drum; said brake band havingone end connected to its associated hydraulic actuator and its other endconnected to an abutment included in said means operatively connectingsaid first friction means to said control valve.

3. In a transmission mechanism, the improvement claimed in claim 1, inwhich said means operatively connecting said first friction means tosaid control valve further includes a pivoted lever having one endengaged with said abutment and its opposite end engaged with a positionadjusting element of said control valve.

4. In a transmission mechanism, the improvement claimed in claim 1,including an engine braking discriminating unit operable responsive tochanges in the direction of torque transmission between said driving anddriven shafts; means connecting said engine braking discriminating unitto said source and in controlling relation with said control valve; saidengine braking discriminating unit, responsive to detection of enginebraking, adjusting said control valve to supply, to the hydraulicactuator of said first friction means, a greatly increased regulatedpressure.

5. In a transmission mechanism, the improvement claimed in claim 4,including means operatively associated with said engine brakingdiscriminating unit and said control valve and operable to increase thepressure regulated by said control valve in substantial correspondencewith an increase in the speed of said driven shaft. I

6. In a transmission mechanism, the improvement claimed in claim 5, inwhich said last-named means is a governor valve connected to said drivenshaft.

7. In a transmission mechanism including a driving shaft, a drivenshaft, and change speed gearing interconnecting the shafts, theimprovement comprising, in combination, said gearing including rotatablemembers controlling the speed ratios between said driving and drivenshafts; respective friction means selectively engageable with saidmembers to arrest rotation thereof to select said speed ratios; atsource of hydraulic fluid under pressure; respective hydraulic actuatorsconnected to said source to control engagement of the associatedfriction means with the respective rotatable members to effect gearchanges; at least a first member of said rotatable members exerting areaction torque on its associated first friction means only whenrotating in a first direction, and exerting substantially no reactiontorque on said first friction means when rotating in the oppositedirection; a control valve regulating the pressure supplied from saidsource to the hydraulic actuator of said first friction means, andnormally maintaining such regulated pressure at a relatively lowpreliminary value; means operatively connecting said first frictionmeans to said control valve and operable, responsive to exertion of areaction torque on said first friction means, to adjust said controlvalve to supply, to the hydraulic actuator of said first friction means,an increased regulated pressure substantially proportional to

1. In a transmission mechanism including a driving shaft, a drivenshaft, and change speed gearing interconnecting the shafts, theimprovement comprising, in combination, said gearing including rotatablemembers controlling the speed ratios between said driving and drivenshafts; respective friction means selectively engageable with saidmembers to arrest rotation thereof to select said speed ratios; a sourceof hydraulic fluid under pressure; respective hydraulic actuatorsconnected to said source to control engagement of the associatedfriction means with the respective rotatable members to effect gearchanges; at least a first member of said rotatable members exerting areaction torque on its associated first friction means only whenrotating in a first direction, and exerting substantially no reactiontorque on said first friction means when rotating in the oppositedirection; a control valve regulating the pressure supplied from saidsource to the hydraulic actuator of said first Friction means, andnormally maintaining such regulated pressure at a relatively lowpreliminary value; and means operatively connecting said first frictionmeans to said control valve and operable, responsive to exertion of areaction torque on said first friction means, to adjust said controlvalve in correspondence with the magnitude of such reaction torque tosupply, to the hydraulic actuator of said first friction means, aregulated pressure adjusted in direct proportion to the magnitude ofsuch reaction torque to obtain full frictional engagement of said firstfriction means with said first rotatable member to arrest rotation ofthe latter; said first rotatable member having a free-wheeling operationwhen rotating in such opposite direction.
 2. In a transmissionmechanism, the improvement claimed in claim 1, in which said firstrotatable member is a drum and said first friction means is a brake bandengageable with said drum; said brake band having one end connected toits associated hydraulic actuator and its other end connected to anabutment included in said means operatively connecting said firstfriction means to said control valve.
 3. In a transmission mechanism,the improvement claimed in claim 1, in which said means operativelyconnecting said first friction means to said control valve furtherincludes a pivoted lever having one end engaged with said abutment andits opposite end engaged with a position adjusting element of saidcontrol valve.
 4. In a transmission mechanism, the improvement claimedin claim 1, including an engine braking discriminating unit operableresponsive to changes in the direction of torque transmission betweensaid driving and driven shafts; means connecting said engine brakingdiscriminating unit to said source and in controlling relation with saidcontrol valve; said engine braking discriminating unit, responsive todetection of engine braking, adjusting said control valve to supply, tothe hydraulic actuator of said first friction means, a greatly increasedregulated pressure.
 5. In a transmission mechanism, the improvementclaimed in claim 4, including means operatively associated with saidengine braking discriminating unit and said control valve and operableto increase the pressure regulated by said control valve in substantialcorrespondence with an increase in the speed of said driven shaft.
 6. Ina transmission mechanism, the improvement claimed in claim 5, in whichsaid last-named means is a governor valve connected to said drivenshaft.
 7. In a transmission mechanism including a driving shaft, adriven shaft, and change speed gearing interconnecting the shafts, theimprovement comprising, in combination, said gearing including rotatablemembers controlling the speed ratios between said driving and drivenshafts; respective friction means selectively engageable with saidmembers to arrest rotation thereof to select said speed ratios; a sourceof hydraulic fluid under pressure; respective hydraulic actuatorsconnected to said source to control engagement of the associatedfriction means with the respective rotatable members to effect gearchanges; at least a first member of said rotatable members exerting areaction torque on its associated first friction means only whenrotating in a first direction, and exerting substantially no reactiontorque on said first friction means when rotating in the oppositedirection; a control valve regulating the pressure supplied from saidsource to the hydraulic actuator of said first friction means, andnormally maintaining such regulated pressure at a relatively lowpreliminary value; means operatively connecting said first frictionmeans to said control valve and operable, responsive to exertion of areaction torque on said first friction means, to adjust said controlvalve to supply, to the hydraulic actuator of said first friction means,an increased regulated pressure substantially proportional to suchreaction torque to obtain full frictional engagement of said firstfriction means with said first rotatable member to arrest rotation ofthe latter; said first rotatable member having a free-wheeling operationwhen rotating in such opposite direction; a primary pressure regulatingvalve connected to said source; said control valve comprising asecondary pressure regulating valve connected to said primary pressureregulating valve; and a tertiary pressure regulating valve connected incontrolling relation to said secondary pressure regulating valve.